Low stress stiffener runout in pi bonded structure

ABSTRACT

A stringer for having a runout with a raised area configured to reduces stress while improving drainage across the runout when utilized in a close structural component of a vehicle such as an aileron of an aircraft. In one or more configurations, the raised area of the runout of the stringer includes multiple tapered surfaces adjacent to one another oriented and configured as ramps to collectively guide water up, over and down the raised area of the stringer.

STATEMENT OF GOVERNMENT INTEREST

This invention was made with Government support under Contract NumberF33657-D-0026 awarded under the U.S. Air Force. The government hascertain rights in this invention.

TECHNICAL FIELD

The field of the embodiments presented herein is directed towarddiscontinuous stringers in aircraft skins having high stresses, and moreparticularly, to configuring stringer runouts to reduce stresses whilealso providing for water drainage across the stringer runouts.

BACKGROUND

Vehicle lifespan may be increased by reducing stress loads uponstructural components of the vehicle. The structural components oftenuse stiffened panels and other structures bonded with ribs and stringers(stiffeners) to prevent the panel from buckling or otherwise failingwhen subjected to compressive loads. While stringers provide adequatereinforcement with respect to compressive loads, the stringer runouts,or areas at which the stringers terminate and interface with ribs, mayexperience premature failure due to local stress concentrations undercertain conditions.

Traditionally, stringers utilize the runouts to terminate the stringersdue to conflict with other structural components, such as the ribs, andthe runouts inherently form local stress concentrations which reduce theuseful life of the panel. Various techniques are used to reduce thelocal stress concentrations. But increasing skin and stringer thicknesscontributes to undesirable increases in cost and weight of thecorresponding panel. Also, increased stiffness typically inducesincreased loads which may lead to premature failures.

Water may collect within the closed periphery of the interior of anassembled structural component. For example, in a vehicle such as anaircraft, water collects between joined upper and lower surfaces of aportion of a wing or a control surface such as flap, aileron, orelevator. A portion of a stringer enclosed within the structuralcomponent may be configured to permit water drainage across the stringerfrom one side to the other. For example, as shown in FIG. 1, a U-shapedcutout or opening may be machined into the web of the stringer that isbig enough to create a water drain path and permit sufficient waterdrainage within the closed interior of the structural component.

Although the U-shaped cutout is needed for water drainage, the U-shapedcutout increases local stresses of the panel. Under flight conditionsthe current configuration of the U-shaped cutout creates a stressconcentration that leads to premature failure of the closed structuralcomponent. Although a U-shaped cutout with a larger radius or curvaturewill reduce peak stress concentrations, the resulting reduced stresseswill still result in earlier fatigue failure. Also, if a U-shaped cutoutwith a larger radius were machined into the stringer to reduce thestress concentrations enough to reduce premature failures, the radius ofthe enlarged U-shaped cutout would be larger than the height of the webof the stringer, which is impractical.

It is with respect to these and other considerations that the disclosureherein is presented.

SUMMARY

It should be appreciated that this Summary is provided to introduce aselection of concepts in a simplified form that are further describedbelow in the Detailed Description. This Summary is not intended to beused to limit the scope of the claimed subject matter.

According to one embodiment disclosed herein, a first stringer isprovided. The first stringer includes a web having a web height and arunout at a distal end of the web. The runout is defined at least by araised area extending beyond the distal end of the web and a tapereddistal edge of the web continuing into the raised area as the web heightdecreases. Opposite sides of the raised area each include an inversetaper such that the raised area widens substantially perpendicular tothe web as the web tapers into the raised area and as the raised areaextends beyond the distal end of the web. The raised area may includemultiple tapered surfaces adjacent to one another oriented andconfigured as ramps to collectively guide water over the raised area.The tapered distal edge of the web may terminate into the raised area orcontinue into a transverse raised portion of the skin of the structuralcomponent.

According to another embodiment disclosed herein, a stringer assembly isprovided. The stringer assembly includes a transverse rib and a firststringer with a web having a web height and a runout at a distal end ofthe web. The runout is defined at least by a raised area extendingbeyond the distal end of the web and a tapered distal edge of the webcontinuing into the raised area as the web height decreases. Oppositesides of the raised area each include an inverse taper such that theraised area widens substantially perpendicularly to the web as the webtapers into the raised area and as the raised area extends beyond thedistal end of the web. The stringer assembly also includes a secondstringer longitudinally aligned with the first stringer. The secondstring includes a web having a web height and a runout at a distal endof the web. The runout is defined at least by a raised area extendingbeyond the distal end of the web and a tapered distal edge of the webcontinuing into the raised area as the web height decreases. Oppositesides of the raised area each include an inverse taper such that theraised area widens substantially perpendicularly to the web as the webtapers into the raised area and as the raised area extends beyond thedistal end of the web. The raised areas of the first and secondstringers continue into transverse raised portions of the skin bonded tothe transverse rib and the distal ends of the first and second stringersare bisected by the transverse rib.

According to yet another embodiment disclosed herein, a method ofreducing stress loads and controlling the drainage of water around astringer is provided. The method includes providing a stringer with aweb having a web height and a runout at a distal end of the web and araised area extending longitudinally and laterally beyond the distal endof the web. The method also includes tapering a distal edge of the weband continuing the distal edge into the raised area as the web heightdecreases and inverse tapering opposite sides of the raised area suchthat the raised area widens substantially perpendicularly to the web asthe distal edge continues into the raised area and as the raised areaextends beyond the distal end of the web. The method may also includeguiding water over the raised area of the stringer wherein the raisedarea provides multiple tapered surfaces adjacent to one another andorienting the tapered surface as ramps to collectively guide the waterover the raised area.

The features, functions, and advantages that have been discussed can beachieved independently in various embodiments of the present disclosureor may be combined in yet other embodiments, further details of whichcan be seen with reference to the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments presented herein will become more fully understood fromthe detailed description and the accompanying drawings, wherein:

FIG. 1 illustrates a perspective view of integrally machined skin anddiscontinuous stringers having a U-shaped cutout in a Pi bonded ribstructure for forming a structural component, and

FIG. 2 illustrates a perspective view of one configuration of integratedskin and stringers with tapered ends bisected by a continuous transversestiffener (rib) in a Pi bonded structure wherein each of the taperedends include a raised area continuing into the structure of the skinbonded to the rib, which is used in association with at least oneembodiment disclosed herein, and

FIG. 3 illustrates a perspective view of another configuration ofintegrated skin and stringers with tapered ends bisected by a continuoustransverse rib in a Pi bonded structure wherein each of the tapered endsinclude a raised area and the distal end of each of the stringers tapersinto the corresponding raised area, which is used in association with atleast one embodiment disclosed herein, and

FIG. 4 illustrates an end view of the configuration of an integratedskin and stringers with the continuous transverse rib of the Pi bondedstructure of FIG. 3, which is used in association with at least oneembodiment disclosed herein, and

FIG. 5 illustrates one configuration of a method for reducing stressloads and controlling the drainage of water around a stringer isprovided according to at least one embodiment disclosed herein.

The plurality of figures presented in this application illustratesvariations and different aspects of the embodiments of the presentdisclosure. Accordingly, the detailed description on each illustrationwill describe the differences identified in the correspondingillustration.

DETAILED DESCRIPTION

The following detailed description is directed to increasing thelifespan of integrally stiffened structures by reducing peak stresseswithout significantly increasing component stiffness or weight. Asdiscussed above, premature failure of the structural components mayoccur at stringer runout locations when subjected to operational loads.Solutions to the premature failure of the stringers due to local stressconcentrations should contemplate weight factors, as well as cost andcomplexity of manufacturing, particularly within the aircraft industry.

Aspects of this disclosure may be used in many types of vehicles suchas, for example, aircraft, spacecraft, satellites, watercraft,submarines, and passenger, agricultural or construction vehicles. Forthe sake of simplicity in explaining aspects of the present disclosure,this specification may utilize an aircraft as the primary example. Theone or more embodiments described below will be described within thecontext of integral structural components for aircraft where thestringers and skin (panel) are manufactured from one solid block ofmaterial and where the stringers are discontinuous stringers bisected bya continuous transverse rib for forming a Pi bonded and closedstructural component. It should be appreciated that the variousembodiments are not limited to these specific components, or to usewithin vehicles such as aircraft. Rather, the concepts described belowmay equally apply to any implementation in which a stringer or similarstiffening component is terminated in a structural component. In thefollowing detailed description, references are made to the accompanyingdrawings that form a part hereof and in which are shown by way ofillustration specific embodiments or examples. Referring now to thedrawings, in which like numerals represent like elements throughout theseveral figures, aspects of the present disclosure will be presented.

In one or more configurations, a milling machine integrally forms theskin with the stringers of one side of the structural component from asingle workpiece. The inside surface of the skin is milled withtransverse raised portions that are continuous and outwardly protrudefrom the inside surface of the skin. The top of each transverse raisedportion includes a continuous groove or slot configured to receive alengthwise edge a rib. The rib is a separate flat metallic componentbonded into the groove of the skin which requires that the stringers bediscontinuous. A second side of the structural component may besimilarly milled from a second workpiece. Two opposing sides of thestructural component are then bonded together by placing the ribsbetween the two opposing sides and within the grooves in a tongue andgroove fashion. This closed metallic structural component is sometimesreferred to as a grid lock assembly or, alternatively, as a Pi bondedstructure, because the end view of each transverse raised portion with agroove protruding from the skin appears to depict the symbol “π”commonly Romanized as “Pi.”

The structural component may be used, for example, as part of the skinof the aircraft. The skin may form part of an aircraft fuselage or wingsuch as an aileron. In the case of an aircraft wing, the stringerstypically run in a span-wise direction from the root of the wing towardits tip. In aircraft construction, a stringer, stiffener or longeron isa thin strip of material, to which the skin of the aircraft may besecured, or is integrally formed with the skin, and sometimes theseterms may be used interchangeably.

For the sake of simplicity in explaining aspects of the presentdisclosure, this specification will proceed utilizing Pi bondedstructures 50, 110 including stringers 52, 112, with runouts 66, 126having raised areas 70, 130 as the primary examples as described ingreater detail below. Throughout the disclosure, a reference to anelement with double reference numbers such as stringers 52, 112 mayrefer to either one or both of the stringer 52 and stringer 112. Also,other elements with double reference numbers within the disclosure suchas the runouts 66, 126 and the raised areas 70, 130, for example, mayrefer to either one or both.

Many of aspects of the present disclosure are not limited to the Pibonded structures 50, 110. The combination of the stringers 52, 112 andthe raised areas 70, 130 may be tailored to have structural stiffnessoptimized for low stresses. Dependent on the thickness of the skin 54,114, the size of the stringers 52, 112, and the spacing between adjacentstringers 52, 112, the configuration of the raised areas 70, 130 may betailored to achieve a stress level which results in the desired fatiguelife for the component. Use of the stringers 52, 112 with the raisedareas 70, 130 increases the lifespan of the integrally stiffenedassembly of the structural component by reducing the peak stresseswithout significantly increasing component stiffness or weight. Forevery 10% the peak stress is reduced the structural component's flighthours before failure is doubled.

FIG. 1 illustrates a perspective view of integrally machined skin 16with discontinuous stringers 12 of a known Pi bonded structure 10 withU-shaped cutouts 14 at the ends of the two longitudinally alignedstringers 12 for relieving local stress concentrations and for providingwater drainage at the interface with the rib 18. Each stringer 12includes a top edge 22 running along the longitudinal length of thestringers 12. The distal end of each web 24 of the stringers 12 includesa substantially straight and vertical end portion 26 that extends downfrom the top edge 22 of each stringer 12 and at least to a midpointalong the height of the distal end of each web 24. The U-shaped cutouts14 are substantially curved or rounded at the bottom in proximity of theskin 16. Below the midpoint of the height of each web 24, the U-shapedcutout 14 begins to curve and may be defined by an arc or segment 30 ofa circle such as a semicircle. The portion of the U-shaped cutout 14opposite the vertical end portion 26 of each stringer 12 continues intothe transverse raised portion 34 of the skin 16. The rib 18 is bondedinto the groove of the transverse raised portion 34.

The dimensions of the U-shaped cutouts 14 are limited to a single passand the radius of the ball-end cutter of the milling machine. The widthof the segment 30 at the bottom of the U-shaped cutout 14 extendslongitudinally from the web 24 and is generally narrow and substantiallyless that the height of the web 24 of the stringer 12. For example, thewidth of the segment 30 longitudinally is generally less than half theheight of the web 24 of the stringer 12. The width of the segment 30 isalso less than the vertical end portion 26 of the distal end of the web24 of the stringer 12.

FIG. 2 illustrates a perspective view of the Pi bonded structure 50 ofan integrally machined skin 54 having discontinuous first and secondstringers 52 with tapered ends bisected by a transverse rib 56 accordingto one or more configurations of the present disclosure. The first andsecond stringers 52 are substantially longitudinally aligned end-to-endwith one another and are integral with the skin 54. The rib 56 iscontinuous and transverse relative to the stringers 52 such that thefirst and second stringers 52 are bisected by the transverse rib 56.Preferably, the stringers 52 are symmetric on either side of the rib 56.

Stringers 52 each include a web 58 having a web height W_(h) and adistal end 60. Each distal end 60 includes a tapered distal edge 62 thatis preferably straight or linear along all or part of its length. Theweb height W_(h) may be the same height along the entire length of thestringer 52 up to the tapered distal edge 62 upon where the web heightW_(h) begins to decrease due to the tapered distal edge 62. The tapereddistal edge 62 of each stringer 52 is preferably straight or linearalong all or most of its length. The web 58 of each stringer 52 istapered by the tapered distal edge 62 to facilitate the load transferfrom the stringers 52 to the skin 54 by providing a gradual increase intransverse bending and axial stiffness and relieving local stressconcentrations.

In one or more configurations, each stringer 52 further includes arunout 66 defined by at least the tapered distal edge 62 of thecorresponding distal end 60 and by the raised area 70 to increase thethickness of the skin 54 extending longitudinally and laterally beyondthe distal end 60 of the stringer 52. The raised area 70 may be referredto as a pad-up area that redistributes the stresses. The tapered distaledge 62 continues into the raised area 70 of each runout 66 as the webheight W_(h) decreases. The tapered distal edge 62 of the web 58transitions from being straight, into the raised area 70, and then fromthe raised area 70 with a curved or arch portion in a convex manner intotransverse raised portion 74 of the skin 54.

Each side of a raised area 70, relative the tapered distal edge,includes a plurality of compound or tapered surfaces 78 adjacent to andtransitioning into one another for defining a gradient of complexgeometry, wherein each of the tapered surfaces 78 is oriented andconfigured to act as upwardly and downwardly inclined ramps, tocollectively guide the distribution of water from one side of thestringer 52, up and over the raised area 70 (or over and down the raisedarea 70 depending on which side of the stringer 52 the water drainsfrom), to the other side of the stringer 52. The tapered surfaces 78 mayalso be referred to as lands. Each side of each raised area 70 mayinclude more or less than the number of tapered surfaces shown in FIG.2.

As shown in FIG. 2, one or more embodiments of one side of each raisedarea 70 includes adjacent tapered surfaces 78 a, 78 b, 78 c, 78 d, 78 e,and 78 f (which may be hereinafter referred to individually orcollectively as tapered surfaces 78) wherein each of the taperedsurfaces 78 a, 78 b, 78 c, 78 d, 78 e, and 78 f is preferably createdfrom multiple cutting tool passes and different tool paths of themilling machine. The other side of the raised area 70 is defined bytapered surfaces 78 that preferably correspond in shape, size andorientation with the tapered surfaces 78 a, 78 b, 78 c, 78 d, 78 e, anda portion of 78 f. The raised area 70 is symmetric about a longitudinalaxis corresponding with the stringer 52. Tapered surface 78 f iscentrally located on the raised area 70 such that half of the taperedsurface 78 f is on one side of the stringer 52 and the other half of thetapered surface 78 f is on the other side of the stringer 52. Also,tapered surface 78 is preferably flat with constant thickness and thetapered surface 78 f is curved in cross section relative thelongitudinal axis corresponding with the stringer 52. The minimumthickness of tapered surface 78 f is the same as the constant thicknessof the surface 78 a. The greatest thickness of the raised area 70 is atthe tapered surface 78 f which is preferably flat in a transverse mannerrelative to the stinger 52. Therefore, the tapered surface 78 f formsthe highpoint or apex of the raised area 70. For example, one path forwater to drain cross the raised area 70 from one side to the other maybegin at the radius curvature 82, up to tapered surface 78 a, ontotapered surface 78 f and then down the other side of the raised area 70.In one or more embodiments, the tapered surfaces 78 b, 78 c and 78 f areintegral with the transverse raised portion 74 of the skin 54 and thetapered surface 78 e is integral with the web 58. In one or moreconfigurations, one or more of the tapered surfaces 78 and/or thetapered distal end 62 are curved.

The raised area 70 with the plurality of tapered surfaces 78 and thetapered distal end 62 are preferably formed with a milling machine,based on parameters input into the milling machine, according togeometry and load requirements of the structural component. Eachstringer 52 with runout 66 and raised area 70 defines an opening forwater drainage larger than that defined by the constant radius ofsegment 30 of the U-shaped cutout 14 of FIG. 1 because the size of theU-shaped cutout 14 is limited by the radius of a single pass of theball-end cutter of the milling machine. Each raised area 70, with theuse of the tapered surfaces 78, defines an opening for water drainagelarger than can be created by a single pass of the ball-end cutter whilealso reducing the load stresses at the ends of the stringers 52 bydistributing the stresses evenly into the skin 54.

Each raised area 70 fans out from the distal end of the stringer 52.Opposite sides of the raised area 70 of each stringer 52 are eachdefined by an inverse taper 80 that is preferably straight or linearalong all or part of its length until in proximity of the transverseraised portions 74 of the skin 54. The raised areas 70 of the stringers52 widen substantially perpendicular to the height of the webs 58 as thewebs 58 taper into the raised areas 70 and also as the raised areas 70extend beyond the distal ends 60 of the stringers 52 into the transverseraised portions 74. Each raised area 70 of the stringers 52 continuesinto opposite sides of the transverse raised portion 74 such that thatthe raised areas 70 are integral with the transverse raised portion 74.The raised area 70 of each stringer 52 continues into the transverseraised portion 74 at the widest width of each raised area 70 so that rib56, along with the transverse raised portions 74 of the skin 54, carry aportion of the loads previously carried by the stringers 52.

In one or more configurations, the web height W_(h) of each web 58 issmallest when the raised area 70 is widest and the tapered distal edge62 of the web 58 begins at a point which substantially corresponds withthe beginning of the inverse taper 80 on the opposite sides of theraised area 70. The inverse taper 80 on each of the opposite sides ofeach raised area 70 correspond with one another such that the degree ofinverse taper on each side of the raised area 70 is approximately thesame.

One or more configurations include a stringer assembly of first andsecond stringers 52 wherein a width of each of the raised areas 70beyond the tapered distal edge 62 of the webs 58 of the first and secondstringers 52 corresponds with the web height W_(h) of each of the webs58 of the first and second stringers 52. One or more otherconfigurations include a stringer assembly of first and second stringers52 wherein a width of each of the raised areas 70 beyond the tapereddistal edge 62 of the webs 58 of the first and second stringers 52 issubstantially equal to the web height W_(h) of each of the webs 58 ofthe first and second stringers 52. One or more other configurationsinclude first and second stringers 52 wherein a width of each of theraised areas 70 beyond the tapered distal edge 62 of the webs 58 of thefirst and second stringers 52 is greater than the web height W_(h) ofeach of the webs 58 of the first and second stringers 52.

The stringer 52 and the skin 54 with transverse raised portions 74 arepreferably milled by a single pass of a ball-end cutter so that theradius of the ball-end cutter defines a radius curvature 82 between theweb 58 of the stringer 52 and the skin 54. Radius curvatures 82preferably extend along both sides of the entire length of each of thestringers 52, including the runouts 66, and along both sides of each ofthe transverse raised portions 74. A single continuous radius curvature82 preferably extends substantially along one side of the web 58 of oneof the stringers 52, along one side of raised area 70, defining one sideof the inverse taper 80, and along one side of a portion of thetransverse raised portion 74 of the skin 54. As best shown in FIG. 2, aportion of a radius curvature 82 forms part of a raised area 70 alongwith the plurality of tapered surfaces 78.

FIG. 3 illustrates a perspective view of an alternative Pi bondedstructure 110 of an integrally machined skin 114 with discontinuousfirst and second stringers 112 having tapered ends bisected by atransverse rib 116. The stringers 112 are substantially longitudinallyaligned end-to-end with one another and integral with the skin 114. FIG.4 illustrates an end view of the configuration of an integrated skin 114and stringers 112 with the continuous transverse rib 116 of the Pibonded structure 110 of FIG. 3. The Pi bonded structure 110 is similarto Pi bonded structure 50 except for the runouts 66, 126 with raisedareas 70, 130 are different.

Stringers 112 each include a web 118 having a web height W_(h) and adistal end 120. Each distal end 120 includes a tapered distal edge 122that is preferably straight or linear along all or part of its length.The web height W_(h) may be the same height along the entire length ofthe stringer 112 up to the tapered distal edge 132 upon where the webheight W_(h) begins to decrease due to the tapered distal edge 132. Thetapered distal edge 132 of each stringer 112 is preferably straight orlinear along all or most of its length.

In one or more configurations, each stringer 112 further includes therunout 126 defined by at least the tapered distal edge 132 of thecorresponding distal end 120 and by a raised area 130 to increase thethickness of the skin 114 extending longitudinally and laterally beyondthe distal end 120 of the stringer 112. The tapered distal edge 132continues into or transitions into the raised area 130 of each runout126 as the web height W_(h) decreases. The tapered distal edge 132 ofthe web 118 tapers away into and terminates at the raised area 130. Thetapered distal edge 132 may have a curved portion 158 such that thelower end of the tapered distal edge 132 is radiused to become tangentwith the raised area 130.

The stringer 112 and the skin 114 with transverse raised portions 144are preferably milled by a single pass of a ball-end cutter so that theradius of the ball-end cutter defines a radius curvature (fillet) 146between the web 118 of the stringer 112 and the skin 114. Radiuscurvatures 146 preferably extend along both sides of the entire lengthof each of the stringers 112, including the runouts 126, and along bothsides of each of the transverse raised portions 144. A single continuousradius curvature 146 preferably extends substantially along one side ofthe web 118 of one of the stringers 112, along one side of raised area130 defining one side of the inverse taper 152, and along one side of aportion of the transverse raised portion 144 of the skin 114. As bestshown in FIG. 3, a portion of a radius curvature 146 forms part of theraised area 130. As best shown in FIG. 4, each raised area 130 above theradius curvature 146 is otherwise preferably flat between each inversetaper 152 and also between the curved portion 158, or otherwise the endof the tapered distal edge 132, and the transverse raised portion 144 inorder to provide the opening for water drainage between the distal end120 of the stringer 112 and the transverse raised portion 144 of theskin 114.

One or more configurations include a stringer assembly of first andsecond stringers 112 wherein a width of each of the raised areas 130beyond the tapered distal edge 132 of the webs 118 of the first andsecond stringers 112 corresponds with the web height W_(h) of each ofthe webs 118 of the first and second stringers 112. One or more otherconfigurations include a stringer assembly of first and second stringers112 wherein a width of each of the raised areas 130 beyond the tapereddistal edge 132 of the webs 118 of the first and second stringers 112 issubstantially equal to the web height W_(h) of each of the webs 118 ofthe first and second stringers 112. One or more other configurationsinclude first and second stringers 112 wherein a width of each of theraised areas 130 beyond the tapered distal edge 132 of the webs 118 ofthe first and second stringers 112 is greater than the web height W_(h)of each of the webs 118 of the first and second stringers 112.

FIG. 5 illustrates a method 200 for reducing stress loads andcontrolling the drainage of water around a stringer 52, 112. Unlessotherwise indicated, more or fewer operations may be performed thanshown in the figures and described herein.

Additionally, unless otherwise indicated, these operations may also beperformed in a different order than those described herein.

The method 200 starts at operation 202 where a stringer 52, 112 isprovided that includes a web 58, 118 having a web height W_(h) and arunout 66, 126 at a distal end of the web 58, 118. At operation 204, themethod 200 provides a raised area 70,130 extending beyond the distal endof the web 58, 118 to widen the runouts 66, 126 for stress reduction,and at operation 206, the method 200 includes tapering a distal edge 62,132 of the web 58, 118 and continuing the tapered distal edge 62, 132into the raised area 70, 130 as the web height W_(h) decreases. Atoperation 208, the method 200 includes inverse tapering opposite sidesof the raised area 70, 130 such that the raised area 70, 130 widenssubstantially perpendicularly to the web 58, 118 as the tapered distaledge 62, 132 continues into the raised area 70, 130 and as the raisedarea 70, 130 extends beyond the distal end of the web 58, 118. Atoperation 210, the method 200 includes guiding water over the raisedarea 70, 130 of the stringer 52, 112. The method 200 where providing theraised area 70, 130, to widen the runouts 66, 126 for stress reductionsmay also include a plurality of tapered surfaces 78 adjacent to oneanother and orienting the tapered surfaces 78 as ramps to collectivelyguide the water over the raised area 130.

The subject matter described above is provided by way of illustrationonly and should not be construed as limiting. Various modifications andchanges may be made to the subject matter described herein withoutfollowing the example embodiments and applications illustrated anddescribed, and without departing from the true spirit and scope of thepresent disclosure, which is set forth in the following claims.

What is claimed is:
 1. A method of reducing stress loads and controllingwater drainage around a stringer, the method comprising: providing astringer comprising a web having a web height and a runout at a distalend of the web; providing a raised area extending longitudinally andlaterally beyond the distal end of the web; tapering a distal edge ofthe web and continuing the distal edge into the raised area as the webheight decreases; inverse tapering opposite sides of the raised areasuch that the raised area widens substantially perpendicularly to theweb as the distal edge continues into the raised area and as the raisedarea extends beyond the distal end of the web; and guiding water overthe raised area of the stringer.
 2. The method of claim 1, whereinproviding the raised area comprises providing a plurality of taperedsurfaces adjacent to one another and orienting the tapered surfaces asramps to collectively guide the water over the raised area.
 3. Themethod of claim 1, further comprising forming a radius curvature in theraised area between the web of the stringer and a skin, wherein theradius curvature extends along a length of the stringer and along atransverse raised portion of the skin bonded to a rib.
 4. The method ofclaim 1, wherein the tapered distal edge of the web terminates into theraised area.
 5. The method of claim 1, wherein the tapered distal edgeof the web continues into a transverse raised portion of a skin.
 6. Themethod of claim 1, wherein inverse tapering the opposite sides of theraised area comprises inverse tapering straight opposite sides of theraised area.
 7. The method of claim 1, wherein tapering the distal edgeof the web comprises tapering the distal edge of the web at a pointsubstantially corresponding with a beginning of the inverse tapering onthe opposite sides of the raised area.
 8. The method of claim 1, whereinthe web height is smallest where the raised area is widest.
 9. Themethod of claim 1, wherein: the stringer comprises a first stringerportion substantially longitudinally aligned with a second stringerportion; a transverse rib bisects the first and second stringerportions; providing the raised area comprises providing a raised area ofthe first stringer portion and providing a raised area of the secondstringer portion; the raised area of the first stringer portion and theraised area of the second stringer portion continue into transverseraised portions of a skin bonded to the transverse rib; and the raisedareas of the first and second stringer portions are widest where theraised areas of the first and second stringer portions continue into thetransverse rib.
 10. The method of claim 1, wherein a skin, transverseraised portions of the skin, the web, and the raised area of thestringer are integrally formed from a single workpiece.
 11. A method ofreducing stress loads and controlling water drainage around a stringer,the method comprising: providing a first stringer substantiallylongitudinally aligned with a second stringer, each of the first andsecond stringers comprising a web having a web height and a runout at adistal end of the web; providing a transverse rib bisecting the firstand second stringers; providing a raised area extending longitudinallyand laterally beyond the distal end of the web of each of the first andsecond stringers; tapering a distal edge of the web of each of the firstand second stringers, and continuing each distal edge into the raisedarea as the web height decreases, wherein the tapered distal edge of theweb of each of the first and second stringers continues into oppositesides of a transverse raised portion of a skin; inverse taperingopposite sides of the raised area of each of the first and secondstringers such that each raised area widens substantiallyperpendicularly to an associated web as the distal edge continues intothe raised area and as the raised area extends beyond the distal end ofthe associated web; and wherein providing the raised area of each of thefirst and second stringers comprises providing a plurality of taperedsurfaces adjacent to one another and orienting the tapered surfaces asramps to collectively guide water over the raised areas of the first andsecond stringers.
 12. The method of claim 11, further comprising forminga radius curvature in the raised area between each web of the first andsecond stringers and a skin, wherein the radius curvature extends alonga length of the first and second stringers and along transverse raisedportions of the skin bonded to a rib.
 13. The method of claim 11,wherein inverse tapering the opposite sides of each of the raised areasthe first and second stringers comprises inverse tapering straightopposite sides of each raised area.
 14. The method of claim 11, whereintapering the distal edge of the web of each of the first and secondstringers comprises tapering the distal edge of the web at a pointsubstantially corresponding with a beginning of the inverse tapering onthe opposite sides of an associated raised area.
 15. The method of claim11, wherein a skin, transverse raised portions of the skin, each web ofthe first and second stringers, and each raised area of the first andsecond stringers are integrally formed from a single workpiece.
 16. Amethod of reducing stress loads and controlling water drainage around astringer, the method comprising: providing a first stringersubstantially longitudinally aligned with a second stringer, each of thefirst and second stringers comprising a web having a web height and arunout at a distal end of the web; providing a transverse rib bisectingthe first and second stringers; providing a raised area extendinglongitudinally and laterally beyond the distal end of the web of each ofthe first and second stringers; tapering a distal edge of the web ofeach of the first and second stringers, and continuing each distal edgeinto the raised area as the web height decreases, wherein the tapereddistal edge of the web of each of the first and second stringersterminates into an associated raised area; inverse tapering oppositesides of the raised area of each of the first and second stringers suchthat each raised area widens substantially perpendicularly to anassociated web as the distal edge continues into the raised area and asthe raised area extends beyond the distal end of the associated web; andwherein providing the raised area of each of the first and secondstringers comprises providing a plurality of tapered surfaces adjacentto one another and orienting the tapered surfaces as ramps tocollectively guide water over the raised areas of the first and secondstringers.
 17. The method of claim 16, further comprising forming aradius curvature in the raised area between each web of the first andsecond stringers and a skin, wherein the radius curvature extends alonga length of the first and second stringers and along transverse raisedportions of the skin bonded to a rib.
 18. The method of claim 16,wherein inverse tapering the opposite sides of each of the raised areasthe first and second stringers comprises inverse tapering straightopposite sides of each raised area.
 19. The method of claim 16, whereintapering the distal edge of the web of each of the first and secondstringers comprises tapering the distal edge of the web at a pointsubstantially corresponding with a beginning of the inverse tapering onthe opposite sides of an associated raised area.
 20. The method of claim16, wherein a skin, transverse raised portions of the skin, each web ofthe first and second stringers, and each raised area of the first andsecond stringers are integrally formed from a single workpiece.